Road vehicles, such as automobiles having a standard mechanical transmission can be started from a standstill, with the motor not running, but the ignition being turned on, by pushing or pulling the vehicle while the transmission is in low gear but is disengaged by means of a clutch. When the pushed or pulled vehicle reaches a sufficient momentum, then the clutch is engaged and the motor of the vehicle becomes turned on. Throughout the specification and the claims this mode of starting the engine of a vehicle is referred to as "push starting".
In hydraulic transmissions a liquid or defined pressure must be available for the throwing into gear of the hydraulic converter, the friction clutch and the individual gears. This pressure is provided by a pump to automatic transmission. However, liquid is delivered by the pump only with the engine running. Therefore the engine cannot be push started in vehicles equipped with hydraulic transmissions.
This problem has been solved by a number of highly reputed manufacturers by installing a second pump to the drive-out shaft of the automatic transmission, which supplies the hydraulic liquid during push starting the engine. However, this solution has the disadvantage of the requirement for and costs of extra parts for this purpose.